1. Field of the Invention
The present invention relates to a method for preparing a titanium-silicalite molecular sieve, and more particular to, a method for preparing a titanium-silicalite molecular sieve with high reactivity and a method for preparing a cyclohexanone oxime using the titanium-silicalite molecular sieve.
2. Description of the Prior Art
Crystalline titanium-silicalite molecular sieves are formed by incorporating titanium into the zeolite structure of silicon dioxide, and have the MFI structures, which are also named as the TS-1 molecular sieves. U.S. Pat. No. 4,410,501 discloses the preparation of this molecular sieve. Such molecular sieve is used as a catalyst in an oxidation reaction, wherein hydrogen peroxide is used as an oxidant. However, the hydrolysis rate of the titanium source is too fast to match the hydrolysis rate of the silicon source, such that the two materials may not be mixed evenly, and the order degree of the material is decreased. Moreover, the titanium source may become anatase, and the catalyst is thus degraded. Therefore, it is important to have even mixing of materials and proper hydrolysis rates of the titanium source and the silicon source, and to avoid the formation of anatase.
Chemical Engineering Journal 156 (2010) 562-570, Journal of Materials Science 37 (2002) 1959-1965, J. Phys. Chem. A 2009, 113, 15006-15015, Ind. Eng. Chem. Res. 48, 4334-4339, 2009 disclose UV-visible diffuse reflectance spectra of TS-1, wherein the peak at 220 nm represents the bonding of titanium-oxygen-silicon, and the peak at 330 nm represents the bonding of titanium-oxygen-titanium. The higher titanium content results in more significant peak at 330 nm. The MFI structure is based on the bonding of titanium-oxygen-silicon, and thus the conventional technology focused on the reduction of the bonding of titanium-oxygen-titanium, and developed the methods for lowering the titanium content. However, the lower titanium content results in fewer activity spots on the TS-1 molecular sieve and lower catalyst activity.
UK Patent GB 2071071 discloses using TEOT (titanium tetraethoxide) as the titanium source for preparing TS-1 catalysts; however, the hydrolysis rate of the TEOT is faster than that of the silicon source, TEOS (silicon tetraethoxide), such that the bonding of titanium-oxygen-titanium is formed, and the titanium content in the molecular sieve structure is reduced. U.S. Pat. No. 4,410,501 discloses that the TEOT is oxidized by hydrogen peroxide into the titanium peroxide solution, which avoids the formation of titanium-oxygen-titanium bonding, before the preparation of TS-1 catalysts. However, U.S. Pat. No. 6,991,678B2 discloses that the titanium peroxide solution is unstable in the basic environment, such as interaction with the neutral or basic template agent.
U.S. Pat. No. 5,885,546 discloses using acetylacetone for preparing TS-1 catalysts to decrease the hydrolysis rate of the titanium source. Accordingly, it is important to have close hydrolysis rates of the titanium source and the silicon source for preparing TS-1 catalysts with a proper titanium-oxygen-silicon structure.
Hence, it is an urgent issue to develop a method for preparing a titanium-silicalite molecular sieve with a high activity so as to improve the usage efficiency of hydrogen peroxide and favor the application in the industry.